The direct drives of NORD drivesystems brought more than just higher reliability and reduced financial and labour expenditure for maintenance activities. The relative investment costs for purchasing new gear units also proved to be lower.Gravel plant cuts costs and reduces maintenance expenditures by using geared motors. In many gravel pits, stone crushing plants and similar operations, motive power for conveyor belts is provided by shaft and belt drives. Until recently, this was the situation at the gravel plant of NorStone AS in Tau, located in the southwest region of Norway. Recently NorStone, a subsidiary of HeidelbergCement AG, decided to change to robust geared motors. This option promised lower investment costs and increased operational reliability, along with better process security. Reduced energy consumption thanks to higher efficiency was also anticipated.NorStone is Norway’s largest producer of gravel products. The company supplies aggregates for concrete and asphalt, pipe cover gravel for coastal regions, and other special products. Each year NorStone’s production facilities produce over 6.6 million tonnes of gravel products in various sorts and quality classes. The demand is large, and even with its present annual production capacity of 2.3 million tonnes of material the Tau plant can scarcely meet the demand. This makes it especially important to ensure that the plant is operational as much as possible and to minimise unplanned downtime.Familiar advantages plus increased reliability with direct drivesGeared motors are actually not new in gravel pits. Direct drives of this sort were commonly used in the 1980s, but in subsequent years many plants changed to belt drives because spare parts for these drives were always quickly available, while manufacturers and suppliers of geared motors were unable to offer stocks of spare parts with the same good availability. "We have found that service and spare parts for geared motors are now available to us very quickly. We hold some parts in stock ourselves, and for all of the rest we have complete trust in NORD Drivesystems as a supplier", explained Ivar Ullestad, Maintenance Manager at Tau, as the reason for going back to the former solution. "This allows the known advantages of drive solutions with geared motors to be fully exploited. In particular, direct drive leads to higher reliability, which means less downtime and therefore less lost production time. Another important aspect is that less maintenance is necessary. In addition to reducing maintenance costs, this increases safety in the plant", added Ullestad.Measurably less wear than with shafts and beltsWorking conditions are a significant factor in such considerations. "You have to bear in mind that we work outdoors all year round. Most of the locations for the conveyor belt drives are open and unprotected. Due to the harsh weather conditions in the west of Norway, with wind, rain and sleet, as well as the dusty and rather unpleasant environment at the site, we try to minimise repair and maintenance times for our maintenance staff." The Tau plant runs seven days a week, 24 hours a day in shift operation. The 168 production hours include 16 hours of scheduled maintenance. The plant is only shut down for the winter break. During this break, annual maintenance inspection and overhaul tasks are performed in two to three weeks. The direct drives have contributed to a distinct increase in reliability, amounting to approximately 4.5 per cent, in the last three years. "We are very satisfied with this trend. With the change from shaft and belt drives to direct drive with geared motors from NORD Drivesystems, in the first place we eliminate the aspect of belt wear, which is considerable. Furthermore, no water or dust can enter the drive mechanism. This means that the decision in favour of compact, robust geared motor units yields clear advantages and has therefore proven to be an intelligent move", summarised Per Thu, Production Manager of the NorStone plant. The direct drives brought more than just higher reliability and reduced financial and labour expenditure for maintenance activities. The relative investment costs for purchasing new gear units also proved to be lower. Replacing a complete package, consisting of a shaft-type gear unit along with belt pulleys, belts, a shed, belt cover and motor, turned out to be more costly than purchasing a comparable geared motor. As a series of periodic gear unit replacements was anyhow in the works, a comprehensive switch from shaft and belt drive to direct drive was a logical choice for Ullestad. He is currently working to standardise drive components. "With a staged cutback in drive systems for the conveyor belts, we are standardising aspects such as motor size, shaft size and drum diameter in order to limit diversity and thereby simplify maintenance, stock management and service. We are also developing backup solutions, which among other things involves keeping components in stock ourselves," according to the maintenance manager.NORD Drivesystems Pvt. Ltd.282/2, 283/2, Village Mann,Tal. Mulshi, Adj. Hinjewadi MIDC IIPune 411057 IndiaSINGH SwetaPhone : 09765490890SSingh@nord-in.comGetriebebau NORD GmbH & Co. KGRudolf-Diesel-Stra?e 122941 Bargteheide/Hamburg, GermanyNIERMANN J?rgPhone : +49(0) 45 32 / 401 – 360Fax : +49(0) 45 32 / 401 – 254Joerg.Niermann@nord.com